Precisely Controlled Methyl Branching in Polyethylene via Acyclic Diene Metathesis (ADMET) Polymerization

A synthetic approach to attain precisely controlled methyl branching in polyethylene is described. Model polymers based on polyethylene have been created using acyclic diene metathesis (ADMET) chemistry as the mode of polymerization. Differential scanning calorimetry (DSC) was employed to examine the thermal behavior (melting point, heat of fusion, glass transition temperature) of five model polyethylene polymers wherein a methyl branch was placed on each 9th, 11th, 15th, 19th, and 21st carbon respectively along the backbone. Melting points and heats of fusion decrease as the frequency of precise methyl branching increases. On the other hand, the β glass transition and its change in specific heat are independent of branch frequency. Comparisons of these model polymers with industrial polyethylene samples demonstrate that this polycondensation approach will provide the basis for a better understanding of the morphology, crystalline structure, and thermodynamics of the crystallization process of the most abundant synthetic macromolecule in the world, polyethylene.